Radio frequency motor control



Dec. 18, 1945. E. L. CRANDELL 2,391,086

RADIO FREQUENCY MOTOR CONTROL Filed Dec. 4, 1945 SDLENDID @oteuted Bee.18 i945 tits Comps Shoe Machinery tjorporatiou, Boston, Mass, acorporation of Delaware Application llecemher l, 1933, Serial No. 512ml((7 1. El t e?) 2 Claims.

invention relates to apparatus utilizing high frequency electrostaticenergy for generat= irig heat in materials advanced therethrough andrelates more particularly to controls for regulat= ing the speed atwhich materials are advanced through such apparatus.

My U. 5. Patent No. 2,32%,668 which issued July 13, 1943, disclosesbonding apparatus utilizing cctrostatic energy from a vacuum tubeoscillator for the generation or" heat for hondiug piles of materialtogether. In such apparatus, t" e amount of heat generated in thematerial heiug heated is directly proportional to the dielectric loss ofthe material. Changes in the dielectric loss in the material beingheated may ice caused by changes in the density, moisture content,thickness or other physical or chemical characistics of the material andthese changes may resuit in some portions of the material being over--heated and other portions being uoderheatecl if the material is advancedat a constant rate through the electrostatic field.

This invention compensates for changes in the dielectric loss oimaterial being advanced through an electrostatic field by varying thespeed of ao'ivauce of the material through the field in accordance withchan es in the dielectric loss of the material, whereby material havinghigher trio losses is exposed for a smaller t he to the electrostaticfield and. material having lower iiielectric losses has longer exposure.

An object of the invention is to improve the quality the bond or"material receiving in an electrostatic field by varying the time ofexposure of the material to the field in accordance with the dielectricloss of the material.

The invention will now he described with reference to the drawing, ofwhich:

Fig. 1 illustrates diagrammatically the electric circuit connections tothe driving motor and electrodes of a roller type bonding pressembodying this invention, and

Fig. 2 is a diagrammatic view of another embodiment of a control circuitwhich may be used with the bonding press of Fig. 1.

With reference first to Fig. l, the base 5 of the press has mountedthereon the four upright supports 6. The metal bars l are attached tothe lower ends or the supports t, and have joumalled therein thebearings 8 which support the cylin drical, metal roller 9.

The Years it of electric insulating material are slidably positionedalong the supports '5. The springs H have their upper ends attached bythe clamps I? to the upper ends of the supports 6 and are attached attheir lower ends to t e insulating bare it and serve to support the barsit on the supports t while at the same time, they bias the bars ittowards the lower "cars l.

The bearings i of the cylindrical, metal -oller it are jourualled in thebar iii. The springs ll thus act to force the rollers and 1163 togetherfor exerting pressure on the work to he oouded as will be described.

The lower roller is rotated through the pulley and belt by the pulley 29 of the electric motor and acts to move work piece therethrough.

Th wori: piece illustrated comprises tw leather with an adhesivethei'ebet ecu.

plies The roller is connected through its bearing i3 and shaft to theelectric couciuc'or is connected to the tool: coil o thvacuum tubeoscillator The metal her i is connected by the electri conductor it tothe center of the tank coil and to ground.

The tank coil is connected at oueehd through the coupling condenser 25to the anode 26 of the tube 2t and through the radio fro cueucy choke itto the positive side of a suitable high voltage direct cu 'eht supply.The other end of the coil 23 is connected through the grid leak shuntedby condenser to the grid of the tube 25. The midpoint Of the coil isconnected to the cathode of the. tube and to the negative side of thedirect cu; a source.

The oscillator circuit described th going is a conventional one and mayt as is Well known those skilled ill the art to a high. frequency whichmay, for example, he megacycles, for establishing an electrostatic fieldbetween therollers 9 and M which act as electrodes.

The electric motor it which advances the work piece through theelectrostatic field, is energized by direct current from the vacuum tuberectifier lhe anode of the rectifier is connected to one end or" thesecondary 3:3 of the transformer The other end of the secondary 3 1 iscon-- nected by the conductor 2% to one supply terminal oi the electricmotor 2i, and to ground.

The primary 3t of the transformer is connested by the conductors 3t andlit to a suitable source of alternating current which may be vol 60cycle.

The primary fit of the filament transformer ti is connected in parallelwith the primary 3? of the transformer 35. The secondary 42 of the 61bypasses radio frequency currents around the 4 motor 2|. The motor thusreceives direct current from the rectifier 32.

The grid 46 of the rectifier is connected by the conductor 48 and thecoupling condenser 49 to the tank coil 23 and receives high frequencyalternating current therefrom.

In operation, as the motor 2| advances the work piece 22 through theelectrostatic field between the roller electrodes 9 and Id, changes inthe dielectric loss in the work piece cause changes in the highfrequency voltage at the tank coil 23. Increases'in the dielectriclossin the work piece will cause reduced high frequency voltages anddecreases in the dielectric loss will cause increases in the highfrequency voltages.

The high frequency alternating currents applied through the conductor 48and coupling condenser 49 to the grid 48 of the rectifier 32 arerectified and provide voltage drops in the radio frequency choke 45 andthe resistor 46 which vary with changes in the voltage of the highfrequency current. These voltage drops bias the grid 46 of the rectifier32 negative. Increases in the grid bia of the rectifier 32 causecorresponding decreases in the direct current voltage delivered by it tothe motor 2| and decreases in the grid bias cause correspondin increasesin the direct current voltage delivered to the motor 2|.

The speed of the motor 2| varies in accordance with the voltage of thecurrent delivered to it by the rectifier 32 so that when the dielectricloss in the Work piece 22 increases, the motor 2| automatically speedsup so that the work piece has a shorter exposure to the electrostaticfield, and when the dielectric loss decreases, the motor 2|automatically slow down so that the work piece is exposed a longer timeto the electrostatic field. Thus regardless of changes in the dielectricloss of the material being bonded, the heat produced therein is thatwhich is desired.

With reference to Fig. 2, the rectifier 32 instead of supplying theenergizing current to the tact arm 53 and the armature The contact arm53 is attached to one end of the plunger 56 of the solenoid 55. Theplunger 56 has mounted thereon the bias spring 55 which tends to restorethe armature 5%, when retracted, to unretracted position.

asonose The energizing winding of the solenoid 55 receives through theconductors 36 and 51, energizing current from the rectifier 32, which isconnected and operated as described in the foregoing except that itsoutput current is supplied to the solenoid 55 instead of the motor 2|.

An increase in the voltage of the current supplied by the rectifier 32to the solenoid 55 and caused as described, by a decrease in thedielectric loss in thework being bonded, causes the solenoid 55 toretract further its plunger 54.

This causes the contact arm 53 to move along the resistor 52 and todecrease the resistance in series with the motor field winding 5| andcauses the motor 2| to slow down. A decrease in the voltage of thecurrent supplied by the rectifier to the solenoid, caused by an increasein the dielectric loss in the work being bonded, causes the fieldstrength of the solenoid to be less so that the spring 56 moves theplunger 54 towards unretracted position, which in turn moves the contactarm 53 to place more resistance in series with the motor field winding5| causing the motor to speed up.

While the work piece being bonded has been illustrated as a continuousply of leather with adhesive therebetween, the material being bonded maybe plastics not requiring adhesives and may be advanced as separateitems as on a conveyor.

While embodiments of the invention have been described for the purposeof illustration, it should be understood that the invention is notlimited to the exact apparatus and arrangements of apparatus illustratedas modifications thereof may be suggested by those skilled in the artwithout departure from the essence of the invention.

What is claimed is:

1. Heating apparatus COmPIlSlI'Ig means including a vacuum tubeoscillator for generating alternating current, means including saidoscillator for establishing an electrostatic field, means for advancinmaterial to be heated through said field, a rectifier, means forsupplying alternating current from said oscillator to said rectifier forrectification, and means including means utilizing rectified currentfrom said rectifier for adjusting the rate of advance of said advancingmeans.

2. Heating apparatus comprising means including a vacuum tube oscillatorfor generating alternating currents, means including said oscillator forestablishing an electrostatic field, means including an electric motorfor advancing material to be heated through said field, a vacuum tuberectifier, means including said rectifier for supplyin rectifiedalternating current to said motor for energizing same, and meansresponsive to variations in the alternating current voltage from saidoscillator for varying .the impedance of said rectifier for varying thevoltage of the current delivered thereby to said motor.

ERVIN L. CRANDELL.

